I think this was mentioned quite often already, but really, characters looking flashy just to signify they're the main character without any reason BEYOND that is just. really not my thing.
Exhibit A: unusual hair colours.
Maybe the heroine has a genetic quirk that made her hair pink (then maybe other characters, even background characters, should have it too. If it's incredibly rare/the protagonist is the only one to have it, make her surroundings react to it - discrimination, curiosity, or plain STARING, whatever, but don't pass it as something usual while it is not). Maybe she just dyed it to look cool/rebellous/unique (again, make people react to it in some way) - JUST PLEASE MAKE ME AWARE that her hair colour has a cause, and maybe even include it in the plot.
Exhibit B: unusual eye colours.
See Exhibit A. Maybe they wear contacts for fun, I don't know, but if no explanation follows, I'll be off and gone.
Exhibit C: inaccurate appearance.
If your setting is Victorian England (which bores me to death because apart from medieval times this seems to be the only period people know about but okay), people won't have green hair, because literally no-one would have even gotten the idea to dye their hair that colour. If they dyed their hair, it was brown/black/blonde/ginger - natural colours. Same with clothing - you wouldn't see anyone running around in hot pants or mini-skirts etc - and please be aware that clothing etc costs actual money, and yes, your clothing actually reflects your income, so if I see a girl that hardly makes a living off being a farmer but has elaborate princess gowns, it's hardly believable.
Exhibit D: basically non-existing amour for women.
Seriously, why the hell are you this horny. Just. Why.
and yes, gosh I really don't like "animal extras" (idk how else to call them) like cat ears, dog tails etc. Just, why? If you make it a new species, okay, but then please go a bit farther than that. Make the cat folk choke up their hair balls.
I generally have the feeling, if the character has to be ~flashy~ in their appearance, they usually are very under-developed and/or uninteresting characters when it comes down to their core. If they're only worth as the main character because they have this special trait, rather sit down and think about your character building than about how to make them stand out even more visually. Why can't a commoner be a main character, with plain looks and just as plain clothes?
If it's in their character to be flashy (because they just have a flashy personality and want to look the way), that's another thing, but then again the character probably is very well thought-out.
Wow what an essay ;u;
(also sorry if I repeated stuff for the nth time)